It is known to provide transportation refrigeration units with two selectively energized rotary shaft prime mover power plants to drive its refrigerant compressor and the fans for the refrigerant evaporating and condensing coils. Usually the first prime mover is an internal combustion engine having a relatively long drive shaft for powering the unit when it is on the move and the second prime mover is an electric motor having a relatively short drive shaft for powering the unit when a source of electric power is available and the unit is stationary on a boat or at a loading dock or the like. It is of course desirable to construct the refrigeration unit in as compact a package as possible and it is the principal object of this invention to provide a compact refrigeration unit containing the two aforementioned selectively energizable prime mover power plants.